Generally, the present invention relates to the field of tissue preservation. In particular, the present invention relates to a solution for prolonged organ preservation, and more particularly to an aqueous salt solution for the preservation of graphs prior to transplantation. The invention also provides a method of preserving or maintaining an organ, comprising contacting the organ with an aqueous salt solution for organ preservation or maintenance.
Many different tissue and organ preservation solutions have been designed, as investigators have sought to lengthen the time that a tissue or organ may remain extra-corporeally, as well as to maximize function of the organ following implantation. Several of the key solutions that have been used over the years include: 1) the Stanford University solution [see, e.g., Swanson, D. K., et al., Journal of Heart Transplantation, (1988), vol. 7, No. 6, pages 456-467 (mentions composition of the Stanford University solution)]; 2) a modified Collins solution [see, e.g., Maurer, E. J., et al., Transplantation Proceedings, (1990), vol. 22, No. 2, pages 548-550; Swanson, D. K., et al., supra (mention composition of modified Collins solution)]; and 3) the University of Wisconsin solution (Belzer, et al., U.S. Pat. No. 4,798,824, issued Jan. 17, 1989). Of those, the University of Wisconsin (UW) solution is currently regarded as the best. (See, e.g., Maurer, E. J., et al., supra).
In addition to the composition of the tissue and organ preservation and maintenance solution, the method of tissue and organ preservation also affects the success of preservation. Several methods of cardiac preservation have been studied in numerous publications: 1) warm arrest/cold ischemia; 2) cold arrest/macroperfusion; 3) cold arrest/microperfusion; and 4) cold arrest/cold ischemia. The first method involves arresting the heart with a warm cardioplegic solution prior to exsanguination and cold preservation, but this method fails because of the rapid depletion of myocardial energy stores during the warm period. The second method, which involves arresting the heart with a cold preservation solution, is better; but continuous perfusion of the heart with preservation solution during the storage period fails because of the generation of toxic oxygen radicals. In addition, the procedure of the second method is cumbersome and does not lend itself to easy clinical use. The third method, first described in the journal Nature in 1972 in a system called xe2x80x9ctrickle perfusion,xe2x80x9d is better but also cumbersome. The fourth method of preservation is that of a cold cardioplegic arrest followed by a period of cold immersion of the heart. The fourth method is currently the standard method of cardiac preservation. This fourth method reliably preserves hearts for periods of up to six (6) hours, but less than four (4) hours is considered ideal for this method. Since a longer preservation time is desirable, attempts have been made to improve preservation solutions in such a way as to reliably preserve hearts and other organs for longer periods of time.
Though the University of Wisconsin (UW) solution is currently the industry standard of organ preservation solutions, it is limited in the length of preservation time that it provides. Other solutions have been proposed (see, for example, U.S. Pat. No. 5,552,267 to Stern), however, these have limited use do to the complicated nature of the composition.
The relationship between the long-term patency and endothelial cell preservation has been established. Endothelial cells are known to be important mediators in regulating platelet, anticoagulant, procoagulant, and fibrinolytic functions. These activities of the endothelium allow for control of blood flow as well as thrombosis or blood clotting when there is endothelial injury. Presently, storage solutions are limited in the length of storage (up to 125 minutes) and protection provided to the endothelium. This time frame is insufficient depending on the type of operation being performed (i.e. whether or not a valve replacement or carotid endarterectomy will be needed along with bypass) and on the surgeon performing the operation.
Currently available storage solutions used during bypass surgery vary from normal saline, to physiological salt solutions, to heparinized blood. These solutions do not provide an adequate environment for endothelial or smooth muscle cell support. Normal saline lacks an energy source such as glucose. The pH of saline solutions tend to be low in the 6 to 7 range which is hostile to these fragile cells. Heparinized blood has only been shown to provide adequate storage of veins only up to 90 minutes. All of the currently available solutions are deficient in the combination of free radical scavengers, antioxidants, and nitric oxide synthase substrates that can provide a protective environment for cellular support during this time period where much damage occurs.
What is needed is a physiological salt solution that would prolong the storage and protection available to harvested bypass conduits and other organs such as those used for transplantation in excess of 24 hours on the basis of cell viability and the integrity of key cell regulatory pathways, including nitric oxide synthesis.
Generally, the present invention relates to the field of tissue preservation. In particular, the present invention relates to a solution for prolonged organ preservation, and more particularly to an aqueous salt solution for the preservation of graphs prior to transplantation. The invention also provides a method of preserving or maintaining an organ, comprising contacting the organ with as aqueous salt solution for organ preservation or maintenance.
Adequate preservation of organs intended for transplantation is critical to the proper functioning of the organ following implantation. This invention concerns an organ preservation or maintenance solution that can preserve organs intended for transplantation for periods of time that are longer than the currently best solution available. In particular, the present invention concerns the preservation of venous and arterial graphs. A longer preservation time is desired to enable cross-matching of donor and recipient to improve subsequent survival, as well as to allow for coast to coast and international transportation of organs to expand the donor and recipient pools. Experimental work for this invention has focused on the heart and heart tissues, but the organ preservation or maintenance solution of the subject invention may be used for other organs, and for tissues and cells, as well.
The organ preservation or maintenance solution of the present invention shows a substantial improvement over the prior art for increasing the preservation time for organs intended for transplantation. (See Experimental section). The organ preservation or maintenance solution of this subject invention shall be referred to as the GALA solution (named after Glutathione, Ascorbic acid, L-Arginine).
The present invention differs from other organ preservation solutions of the prior art in a number of respects. In our experiments, none of these solutions were able to preserve the structural integrity and function of saphenous vein endothelium for more than 2 hours. The present invention includes NOS substrates and antioxidants and is simple to prepare, being composed of a limited number of ingredients. Additionally, it does not require the elimination of sodium, calcium and chloride from the solution, as does at least one prior art solution (see U.S. Pat. No. 5,552,267 to Stern, et al.). In these regards, the present invention is improved over prior art compositions in that it permits the viability of tissue to be maintained longer than in traditional solutions and it is easier to prepare.
The GALA solution of the present invention is based on Hank""s balanced saline solution. Hank""s balanced salt solution (HBSS) is a commercially available physiological salt solution containing D-glucose 1 g/L, calcium chloride (anhydrous) 0.14 g/l, potassium chloride 0.4 g/l, potassium phosphate 0.06 g/l, magnesium chloride.6H2O 0.1 g/l, magnesium chloride.7 H2O 0.1 g/l, sodium chloride 8 g/l, sodium bicarbonate 0.35 g/l, and sodium phosphate 0.048 g/l. The present invention modifies HBSS by the addition of ascorbic acid (vitamin C), reduced glutathione, L-arginine, and heparin to a final concentrations of about 500 xcexcM, 1000 xcexcM, 500 xcexcM, and 50 Units/ml, respectively. The pH is then adjusted to 7.4 using 10 M sodium hydroxide. To date, no known preservation solution for harvested veins and arteries has been enhanced with ascorbic acid, glutathione, L-arginine, and heparin in an attempt to prevent endothelial injury. This new solution provides free radical scavengers, antioxidants, an NO substrate, a reducing agent, an energy source (glucose), an anti-coagulant, and physiological concentrations of electrolytes and buffers. As demonstrated in the Experimental section (below), the solution has the unexpected benefit of providing a greatly extended preservation time over the available prior art preservation solutions.
The present invention is not limited to the compositions listed above. Adenosine may be added as a supplemental energy source. Adenosine may be added a concentration of about 500 xcexcM-5000 xcexcM. Additionally, Lacidipine, a vasorelaxant calcium channel blocker, may be added to GALA in the final concentration of about 1 pM-1 mM. Additionally still, vasoactive intestinal peptide (VIP) may be added to GALA in the final concentration of about 1 xcexcM-1 mM. Additionally still, Endothelin receptor agonists/antagonists (ETa and ETb-receptors) may be added to GALA. Although the present invention is not limited to any particular mechanism, endothelin receptor agonists/antagonists work as vasocontractors and vasorelaxants, respectively. Furthermore, an anticoagulant need not be added, for example, in situations where the tissue or organ has been perfused of blood. Further still, glutathione need not be added because, for example, it is partly synergistic with ascorbic acid. Therefore, it is contemplated that a minmal formulation of the present invention would be HBSS with ascorbic acid and L-arginine added in to the concentrations listed above.
The present invention is not limited to any particular concentration of the ingredients listed above. In one embodiment, the concentration of ascorbic acid is between about 25-1000 xcexcM. In another embodiment, the concentration of glutathione is between about 50-2000 xcexcM. In yet another embodiment, the concentration of L-arginine is between about 250-2000 xcexcM. In still yet another embodiment, the concentration of heparin is between about 50-250 units/l. The present invention is not limited to any particular pH. In one embodiment the pH of the solution is between about pH 6.6-8.0. More preferably, the pH is between about pH 7.0-7.6. The present invention is not limited to any particular anticoagulant. In one embodiment, the anticoagulant is heparin. In another embodiment, the anticoagulant is hirudin. The solution of the present invention may contain certain bacteriostats. The bacteriostat may be selected from a group comprising penicillin and cerfazolin. Other bacteriostats may be used. Selection of a bacteriostat may be determined at the time of practicing the invention. For example, allergies may be taken into account when selecting a bacteriostat.
The present invention is not limited to use with a particular tissue, organ or cell type. For example, the invention may be used with harvested saphenous veins, epigastric arteries, gastroepiploic arteries and radial arteries used in coronary bypass grafting (CABG). The present invention may also be used to maintain organs and tissue during transplant operations. The present invention is not limited to any particular tissue or organ. For example, it is contemplated that such organs or tissues may be heart, lungs, kidney, brain, muscle grafts, skin, intestine, bone, appendages, eyes, etc or portions thereof. Additionally, the present invention may be used as an in situ tissue or organ preservative. It is contemplated that the solution of the present invention be used to wash and bath tissues and organs that have not been removed from the patient. For example, it is contemplated that the present invention be used during cardioplegia. It is also contemplated that the present invention be used in, for example, emergency procedures where a tissue or organ may need to be bathed to preserve it until surgery or other medical attention can be obtained. In this regard, the solution may be made available to emergency medical personnel both in hospital settings and xe2x80x9cin the fieldxe2x80x9d (i.e., in ambulances or in temporary emergency medical facilities).
The present invention contemplates the present invention may be an aqueous solution or the present invention may be composed of powders and concentrated solutions that could be mixed with sterile water, as needed. The present invention also contemplates that the invention may be composed of a quantity of HBSS along with a supplement package that may be mixed with the HBSS.
The present invention contemplates an aqueous solution for organ and tissue preservation, comprising: a) calcium ions; b) D-glucose (from about 50 mM to about 120 mM); c) potassium ions (from about 100 mM to about 250 mM; derived from compounds selected from the group consisting of potassium chloride, and potassium phosphate); d) magnesium ions (from about 2 mM to about 20 mM; derived from compounds selected from the group consisting of magnesium sulfate, and magnesium chloride); e) sodium ions; f) ascorbic acid in a concentration of about 25-1000 xcexcM; g) glutathione in a concentration of about 50-2000 xcexcM; h) L-arginine in a concentration of about 250-2000 xcexcM; i) an anticoagulant (selected from heparin and hirudin) at a concentration sufficient to substantially inhibit blood coagulation (for heparin this would be from about 50 units/l to about 250 units/l); and j) a buffer (the buffer is selected from the group consisting of sodium phosphate and sodium bicarbonate) in an amount sufficient to maintain the pH of said aqueous organ preservation solution at about 6.8 to 8.0.
The present invention contemplates an aqueous solution for organ and tissue preservation, comprising: a) calcium ions; b) D-glucose (from about 50 mM to about 120 mM); c) potassium ions (from about 100 mM to about 250 mM; derived from compounds selected from the group consisting of potassium chloride, and potassium phosphate); d) magnesium ions (from about 2 mM to about 20 mM; derived from compounds selected from the group consisting of magnesium sulfate, and magnesium chloride); e) sodium ions; f) ascorbic acid in a concentration of about 25-1000 xcexcM; g) glutathione in a concentration of about 50-2000 xcexcM; h) L-arginine in a concentration of about 250-2000 xcexcM; i) an anticoagulant (selected from heparin and hirudin) at a concentration sufficient to substantially inhibit blood coagulation (for heparin this would be from about 50 units/l to about 250 units/l); and j) a buffer (the buffer is selected from the group consisting of sodium phosphate and sodium bicarbonate) in an amount sufficient to maintain the pH of said aqueous organ preservation solution at about 6.8 to 8.0; and k) tissue. Additionally, the present invention contemplates that the tissue is saphenous vein.
The present invention contemplates a method for preserving tissue comprising:
i. providing a tissue; ii. contacting said tissue with a solution comprising: a) calcium ions in an amount sufficient to support intracellular function and maintenance of cellular bioenergetics; b) D-glucose in an amount sufficient to support intracellular function and maintenance of cellular bioenergetics; c) potassium ions in an amount sufficient to support intracellular function and maintenance of cellular bioenergetics; d) magnesium ions in an amount sufficient to support intracellular function and maintenance of cellular bioenergetics; e) sodium ions in an amount sufficient to support intracellular function and maintenance of cellular bioenergetics; f) ascorbic acid in a concentration of about 25-1000 xcexcM; g) glutathione in a concentration of about 50-2000 xcexcM; h) L-arginine in a concentration of about 250-2000 xcexcM; i) an anticoagulant at a concentration sufficient to substantially inhibit blood coagulation; and f) a buffer in an amount sufficient to maintain the average pH of said aqueous organ preservation solution at about a physiological ph or above.
Additionally, the present invention contemplates a kit for the preparation of an organ preservation solution comprising: i. a container; ii. an aqueous solution disposed within said container wherein said solution comprises; a) D-glucose; b) calcium chloride; c) potassium chloride; d) potassium phosphate; e) magnesium chloride 6.H2O; f) magnesium chloride 7.H2O; g) sodium chloride; h) sodium bicarbonate; and sodium phosphate; iii. a supplement for introduction into said solution comprising; j) ascorbic acid; k) glutathione; l) L-arginine; and m) heparin.
Furthermore, the present invention contemplates a kit for the preparation of an organ preservation solution comprising: i. a container; ii. reagents deposited in said container, said reagents comprising, a) D-glucose; b) calcium chloride; c) potassium chloride; d) potassium phosphate; e) magnesium chloride 6.H2O; f) magnesium chloride 7.H2O; g) sodium chloride; h) sodium bicarbonate; and i) sodium phosphate; j) ascorbic acid; k) glutathione; l) L-arginine; m) heparin; and n) sterile water.
The present invention contemplates a composition comprising an aqueous salt solution comprising an antioxidant, glutathione, an L-amino acid and an anticoagulant. Additionally, the present invention contemplates the composition wherein it also comprises isolated tissue. Particularly, the isolated tissue may be a vein, and more particularly, a saphenous vein.
The composition of the present invention may also comprise glucose. Furthermore, the antioxidant of the present invention may be ascorbic acid. Yet further still, the concentration of the ascorbic acid is about 25-1000 xcexcM. Even further still, the concentration of the glutathione is of about 50-2000 xcexcM. Even further still, the L-amino acid is L-arginine. Even further still, the L-arginine is present in a concentration of about 250-2000 xcexcM. Even further still, the anticoagulant is selected from the group consisting of heparin and hirudin. Even further still, the anticoagulant is heparin, and wherein said heparin is present in a concentration of between about 50 units/ml and about 250 units/ml.
The present invention contemplates a composition comprising an isolated tissue in an aqueous salt solution comprising an antioxidant, glutathione, an L-amino acid and an anticoagulant. Further still, the tissue is an isolated vein. Even further still, the vein is a saphenous vein. Even further still, the antioxidant is ascorbic acid and the ascorbic acid is present in a concentration of about 25-1000 xcexcM. Even further still, the glutathione is present in a concentration of about 50-2000 xcexcM. Even further still, the L-amino acid is L-arginine and is present in a concentration of about 250-2000 xcexcM. Even further still, the anticoagulant is selected from the group consisting of heparin and hirudin. Even further still, the anticoagulant is heparin, and wherein said heparin is present in a concentration of between about 50 units/ml and about 250 units/ml.
The present invention contemplates a composition comprising an isolated human tissue in an aqueous salt solution comprising an antioxidant, glutathione, an L-amino acid and an anticoagulant. Further still, the tissue is an isolated human vein. Even further still, the vein is a saphenous vein. Even further still, the antioxidant is ascorbic acid and the ascorbic acid is present in a concentration of about 25-1000 xcexcM. Even further still, the glutathione is present in a concentration of about 50-2000 xcexcM. Even further still, the L-amino acid is L-arginine and is present in a concentration of about 250-2000 xcexcM. Even further still, the anticoagulant is selected from the group consisting of heparin and hirudin. Even further still, the anticoagulant is heparin, and wherein said heparin is present in a concentration of between about 50 units/ml and about 250 units/ml.
The present invention contemplates a method, comprising: a) providing i) an isolated tissue and ii) an aqueous salt solution comprising an antioxidant, glutathione, an L-amino acid and an anticoagulant; and b) contacting said isolated tissue with said aqueous salt solution. Furthermore, the tissue is an isolated vein. Even further still, the is a saphenous vein. Even further still, the antioxidant is ascorbic acid and the ascorbic acid is present in a concentration of about 25-1000 xcexcM. Even further still, the glutathione is present in a concentration of about 50-2000 xcexcM. Even further still, the L-amino acid is L-arginine and is present in a concentration of about 250-2000 xcexcM. Even further still, the anticoagulant is selected from the group consisting of heparin and hirudin. Even further still, the anticoagulant is heparin, and wherein said heparin is present in a concentration of between about 50 units/mL and about 250 units/mL.
FIG. 1 shows the viability of human saphenous vein stored in various storage solutions.
FIG. 2 shows the effects on endothelial nitric oxide synthase (eNOS) activity after 5 hours of storage in HBSS vs. GALA solution.
FIG. 3 shows a comparison of cell viability of human saphenous veins stored in HBSS verses GALA solution.
FIG. 4 shows cell viability of a human saphenous vein following 24 hours of storage in GALA solution.
FIG. 5 shows immunofluorescence labeling of SVG stored in GALA and HLS for 3 hours.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described. For purposes of the present invention, the following terms are defined below.
As used herein, the term xe2x80x9cpatientxe2x80x9d includes members of the animal kingdom including but not limited to human beings.
As employed herein, xe2x80x9corganxe2x80x9d includes, but is not limited to, the heart, veins, arteries, lungs, liver, pancreas and the kidneys. Portions of organs are also contemplated.
As used herein, xe2x80x9csterile waterxe2x80x9d includes, but is not limited to, (a) sterile water for injection, USP, (b) sterile distilled deionized water, and (c) sterile water for irrigation.
As used herein, xe2x80x9ccardioplegiaxe2x80x9d includes, but is not limited to, paralysis of the heart.
As used herein, xe2x80x9cmoderate hypothermiaxe2x80x9d is about 10xc2x0-21xc2x0 C.
As used herein, an xe2x80x9cantioxidantxe2x80x9d is a substance that, when present in a mixture or structure containing an oxidizable substrate biological molecule, delays or prevents oxidation of the substrate biological molecule. For example, ascorbic acid and . . . are antioxidants.
xe2x80x9cBalanced salt solutionxe2x80x9d is defined as an aqueous solution that is osmotically balanced to prevent acute cell or tissue damage.
xe2x80x9cBuffered salt solutionxe2x80x9d is defined as a balanced salt solution to which chemicals have been added to maintain a predetermined physiological pH range.
xe2x80x9cGraftxe2x80x9d is defined as tissue that is transplanted or implanted in a part of the body to repair a defect.
xe2x80x9cHarvested bypass conduitxe2x80x9d is defined as a surgically installed alternate route for the blood to bypass an obstruction.
xe2x80x9cSolution of cardioplegiaxe2x80x9d is defined as a solution that aids in the preservation of the heart during transport or surgery.
xe2x80x9cCellular reducing agentxe2x80x9d is defined as an a substance that loses electrons easily thereby causing other substances to be reduced chemically.
Generally, the present invention relates to the field of tissue preservation. In particular, the present invention relates to a solution for prolonged organ preservation, and more particularly to an aqueous salt solution for the preservation of graphs prior to transplantation. The invention also provides a method of preserving or maintaining an organ, comprising contacting the organ with as aqueous salt solution for organ preservation or maintenance. As such, the present invention is a novel solution that greatly increases the length of time the tissue or organ may remain out of the body.
The organ preservation or maintenance solution may further comprise a reducing agent in an amount sufficient to help decrease reperfusion injury secondary to oxygen free radicals. The role of glutathione as a cellular reducing agent and L-arginine as the substrate for nitric oxide synthase has been well established. Studies have shown that the oral administration of a glutathione substrate improved endothelial dependent blood flow in patients with coronary artery disease.
The organ preservation or maintenance solution may further comprise an antioxidant in an amount sufficient to help decrease reperfusion injury secondary to oxygen free radicals. The antioxidant is selected from the group consisting of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), Vitamin C (ascorbic acid), Vitamin E, or suitable combinations thereof. Other suitable antioxidants may be used. In a preferred embodiment, the antioxidant is butylated hydroxyanisole (BHA) at a concentration range from about 25 microM to about 100 microM, alone or in combination with butylated hydroxytoluene (BHT) at a concentration range from about 25 microM to about 100 microM.
Currently, the protective role of ascorbic acid on endothelial cells is being investigated. Ascorbic acid is known to reduce platelet activation and leukocyte adhesion which are important events in the development of atherosclerosis. Ascorbic acid is also thought to contribute to the reduction in smooth muscle proliferation which is a key component of vein graft failure. Work by Jones and colleagues examined the protective effect of ascorbic acid by showing decreased adherence of neutrophils to the endothelium and free radical scavenging in human umbilical vein endothelial cells (HUVEC). Utoguchi and colleagues showed a decrease in endothelial layer permeability via ascorbic acid-mediated collagen synthesis in HUVEC monolayers. Adams and colleagues observed similar reductions in neutrophil-endothelial cell interactions after oral administration of L-arginine in cigarette smokers.
The organ preservation or maintenance solution may further comprise an anticoagulant in an amount sufficient to help prevent clotting of blood within the capillary bed of the organ. The anticoagulant is selected from the group consisting of heparin or hirudin. Other suitable anticoagulants may be used. In a preferred embodiment, the concentration of heparin ranges from about 50 units/l to about 250 units/l.
Anticoagulants are believed to help in preventing clotting of blood within the capillary bed of the preserved organ. Specifically, anticoagulants are believed to help prevent a total organ no-reflow phenomenon at the level of the microcirculation, which would be undesirable following re-implantation and could result in graft failure. Anticoagulants are believed to be helpful in ensuring that thrombosis does not occur during or after preservation, so that nutrient delivery and toxin removal can proceed.
The present invention contemplates a solution for tissue and organ preservation that is superior to prior art solutions in both the length of time it is able to preserve the tissue or organ, and in its ease of preparation. In one embodiment, the solution is based on HBSS. However, other solutions may be utilized as the basis of the tissue and organ preservation solution of the present invention. Any balanced saline solution could be used. For example, phosphate buffered saline, Ringer""s solution, culture medias and cardiopeligic solutions could be used.
The present invention may be used as a cardioplegic solution. In this regard, the present solution would be administered to the patient""s chest cavity after the heart was paralyzed by, for example, an injection of a potassium enriched solution. After the heart has depolarized, the chest cavity would be flooded with the solution of the present invention, or with an available cardioplegic solution with added glutathione, L-arginine, heparin and ascorbic acid. Additionally, the potassium concentration would be monitored and supplemented as necessary to maintain cardioplegia. In another embodiment, the present invention provides a solution for cardioplegia during cardiac surgery and a solution for preserving a patient""s heart for transplantation. Cardioplegia involves arresting the patient""s heart or harvesting the patient""s organ, perfusing the heart or organ with an aqueous solution of the present invention, and removing at least a substantial portion of the solution from the heart or organ to effect the removal of waste products from the heart or organ. Additionally, the present may be used for tissue and organ preservation for organs that are still within the patient""s body or for tissues and organs that have been removed (for example, for transplantation). In this regard, the present invention may be used as a storage solution after removal of the tissue or organ or as a transportation solution for organs that need to be transferred to a new location for the transplantation to take place (for example, for transport of a heart, kidney or liver from a donor to a recipient). The present invention makes the transport of organs over much longer distances than can presently be accomplished.
Live-Dead assay kit (calcein AM/ethidium homodimer) was obtained from Molecular Probes, Eugen, Oreg. Membrane permeable 4,5-diaminofluorescein diacetate (DAF-2/DA) was purchased from Calbiochem, La Jolla, Calif. Hank""s balanced salt solution (HBSS), Minimum essential medium (MEM) and RPMI 1640 medium were obtained from GibcoBRL, Grand Island, N.Y. HLS solution (heparin, 40 units/ml; lidocain, 0.0016%; saline, 0.9% NaCl) was from the Clinical Pharmacy at VA Medical Center, West Roxbury, Mass. L-arginine, reduced glutathione, L-ascorbic acid, bradykinin and Nw-nitro-L-arginine (LNNA) were purchased from Sigma Chemical Co., St. Louis, Mo. Specially designed chambers used for inverted microscopy consisting of a sterile 35 mm petri plate with a No. 1.5 coverslip sealed over a 10 mm hole in the bottom of the petri plate were obtained from MetTek Corp., Ashland, Mass.